The present invention relates to an expansible anchoring plug for anchoring in pre-drilled holes by impact. More particularly, the invention relates to anchoring plugs to be anchored in pre-drilled holes having a widened undercut portion.
Expansible anchoring plugs of the foregoing type comprise an expansible sleeve which has an internal bore and which also has elongated slots over. the part of its length, which slots form expansible segments, and an expander body, normally of conical shape. The expansible sleeve can be anchored in the pre-drilled hole by driving it the expander body which is positioned at the bottom of the drilled hole.
Expansible anchoring plugs anchored in a support structure, such as a wall, and receiving a screw for fastening an article to the support structure of the type under discussion have been disclosed in some applicant's U.S. patents, for example U.S. Pat. No. 4,185,536.
An expansible fixing plug of the foregoing type for anchoring by impact has been also disclosed in German Offenlegungsschrift No. 31 71 581. Compared with expansible anchoring plugs for anchoring by impact which are anchored by driving an expander pin from the front end through an internal bore of the expansible anchoring plug, driving an expansible sleeve onto an expander body located at the bottom of the pre-drilled hole has the advantage that the maximum size of the expander body can correspond to the diameter of the cylindrical portion of the pre-drilled hole formed in the anchoring material. A considerably higher degree of expansion is thus achieved, which, when such an expansible anchoring plug for anchoring by impact is anchored in a drilled hole, which is flared or widened at the bottom, is required for this widened undercut portion to be filled up. The mating fit of the expansible anchoring plug, which can thereby be achieved in this widened undercut portion results, on the one hand, in considerably higher holding values and, on the other hand, in an increased reliability, particularly in case if any cracks run through the hole in the supporting structure.
Inasmuch as theexpansible sleeve is less securely braced in an undercut hole of the support structure, and since the expander cone tapers towards the bottom of the pre-drilled hole, the expansible segments may, however, be pulled off the expander cone by a tractive force acting on the expansible sleeve. The increased holding force can therefore only be achieved if this slipping-off be prevented.